Hi,
For me, 2 contexts is enough, and I agree with the reasoning behind it
from my experience as well.
- Zach
Jonathan Hui wrote:
In moving the HC draft from -00 to -01, we added support for multiple
compression contexts so that more than one prefix (other than
link-local) can be compressed.
The obvious question now is how many contexts are enough? It is clear
that two contexts are useful (one for the 6LoWPAN and another for the
common destination that all nodes may be sending to). But should we add
more?
Some thoughts:
- Fewer contexts allow the HC encoding to use fewer bits in identifying
the context in use.
- Specifying support for X contexts requires nodes to allocate enough
memory to maintain X contexts (ip addresses, timers, etc.).
- Additionally, we cannot simply say that we will change X to some
larger Y at some future date since the nodes that only support X will
not be able to support Y > X contexts.
- One argument for supporting more contexts is that it allows network
renumbering while allowing all nodes to communicate with compressed
addresses. My thought, however, is that renumbering of 6LoWPAN networks
should be rare and when they do occur it is okay to incur some extra
cost and communicate with full addresses during that time.
So my thought is to keep the number of supported contexts small (2).
What do other people think?
--
Jonathan Hui
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Zach Shelby
Head of Research
Sensinode Ltd.
Kidekuja 2
88610 Vuokatti
FINLAND
mobile: +358 40 7796297
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